The present invention relates to a process for the preparation of a diol. The diol may be used subsequently used as a monomer for the preparation of a polymeric device or material such as a hemocompatible coating, medical device, water soluble polymer material, paint, water borne coating or an ocular device (such as a contact lens).
Polymers made from polymerisable monomers have wide spread applications. For example, polymers are used as additives for coating applications, such as paints and adhesives. Polymers are also used to prepare lenses, such as contact lenses.
Polymers are prepared by polymerising one or more types of polymerisable monomers, such as by emulsion polymerisation, solution polymerisation, suspension polymerisation or bulk polymerisation. The monomer(s) may be polymerised in the presence of optional ingredients such as any one of emulsifiers, stabilisers, surface active agents, initiators (such as photoinitiators), inhibitors, dispersants, oxidising agents, reducing agents, viscosity modifiers, catalysts, binders, activators, accelerators, tackifiers, plasticizers, saponification agents, chain transfer agents, surfactants, fillers, dyes, metal salts, and solvents.
There are numerous references on polymerisation of polymerisable monomers. For example, some teachings may be found in xe2x80x9cEmulsion Polymerization: Theory and Practicexe2x80x9d by D. C. Blackley (published by Wiley in 1975) and xe2x80x9cEmulsion Polymerizationxe2x80x9d by F. A. Bovey et al. (published by lnterscience Publishers in 1965). For example, a polymer can be prepared from monomers such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, styrene, butadiene, ethylene, vinyl acetate, vinyl esters, C9, C10 and C11 tertiary monocarboxylic acids, vinyl chloride, vinyl pyridine, vinyl pyrrolidine, vinylidene chloride, acrylonitrile, chloroprene, acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaric acid.
Examples of further teachings on polymerisation of polymerisable monomers may be found in xe2x80x9cVinyl and Related Polymersxe2x80x9d by C. E. Schildknecht (New York: John Wiley and Sons 1952) and xe2x80x9cMonomeric Acrylic Estersxe2x80x9d by E. H. Riddle (New York: Reinhold Publishing Corp. 1954), and by A. G. Alexander (J. Oil Colour Chemists"" Association [1962] 45 12) and G. G. Greth and J. E. Wilson (J. Appl Polymer Sci [1961] 5 135).
More recent teachings regarding polynerisation methods may be found in EP-A-0622378, EP-A-0634428, EP-A-0623632, EP-A-0635522, EP-A-0633273, EP-A-0632157, EP-A-0630908, EP-A-0630641, EP-A-0628614, EP-A-0628610, EP-A-0622449, EP-A-0626430 and EP-A-0625529.
As mentioned above, one particular application of polymers is in the preparation of lenses, especially contact lenses or intraocular lenses. Examples of teachings for the preparation of contact lenses may be found in EP-A-0359539, which discloses a method of forming a soft contact lens. Other documents that describe the preparation of contact lenses include WO-A-9502617 which discloses a contact lens made from a vinyl polymer bearing phosphonium groups, JP-A-06313009 which discloses a contact lens made from a polymer having a terminal phosphoryl-choline group, WO-A-9429756 which discloses a gas permeable ocular lens made from a block copolymer and a second polymer component, WO-A-9409042 which discloses a contact lens comprising polymer and a UV absorbing constituent, and WO-A-9211407 which discloses a tinted contact lens comprising a polymer and a dye wherein the lens is prepared by incorporating a dye into a hydrophilic polymer while the polymer is being formed. Further documents describing preparing contact lenses and the like from polymerisable monomers include EP-A-0574352, EP-A-0439394, EP-A-0378511 and EP-A-0424520.
Whilst polymers can be fairly easily prepared from polymerisable monomers there can be a problem in reliably and cheaply obtaining suitable monomers in a satisfactory pure form. In this regard, many desired polymerisable monomers are supplied with impurities. These impurities can be detrimental to the final product and so they have to be eliminated before the polymerisation reaction to form the desired polymer.
Impurities which is particularly problematic are compounds which act as cross-linkers during the polymerisation of the monomer. The presence of cross-linkers prevents and/or inhibits the formation of straight chain polymers. Moreover, the presence of cross-linkers in a monomer may prevent the solubilisation of polymers formed therefrom.
Another example of such a monomer is glyceryl methacrylate (GMA) which is a preferred monomer for preparing contact lenses. Examples of documents mentioning the use of such a monomer include U.S. Pat. No. 5,236,969, JP-A-04335007, GB-A-2180243 and EP-A-0100381. There are two major problems with GMA. First, the impurities often vary from batch to batch and so make it difficult to have a standard purification protocol. Second, GMA is a very expensive monomer.
There have been attempts to prepare GMA from other monomers, such as isopropylideneglyceryl methacrylate (IPGMA). One such process for preparing GMA is disclosed in U.S. Pat. No. 4,056,496 wherein the process includes reacting IPGMA with sulphuric acid and hydroquinone for a period of 16 hours.
Another process for preparing GMA, also mentioned in U.S. No. 4,056,496, includes the hydrolysis of glycidyl methacrylate (GYMA) by treating GYMA with concentrated sulphuric acid for 6 days (M. F. Refojo [1965] Journal of Polymer Science 9 pp 3161-3170). This process is particularly disadvantage because the addition of mineral acid to GMA may result in the formation of glyceryl dimethacrylate which is a cross-linker, and various other dimethacrylates.
The distillation of GMA to prepare purified GMA is also practised in the art. Distillation is however both difficult and costly. GMA is high boiling and therefore costs of distillation are high. Distillation typically gives losses of 15-20% of the product to be purified. Moreover, GMA may polymerise during distillation and valuable monomer lost. Yet further, the equipment which may be required to perform the distillation e.g. falling film evaporator, is expensive.
Clearly these prior art methods are very labour intensive and include the use of hazardous chemicals, including toxic chemicals and flammable solvents, and hazardous process steps.
Further prior art methods for preparing GMA polymers are disclosed in U.S. Pat. No. 4,338,419, FR 8207595, WO 93/0841 and Ezrielev et al, Vysokomol. Soedin, Ser. B, 20(10), 777-9, Hild, Makromol. Chem, 177, 1947-1972 (1976) and Beinert et al, Die Makromolekulare Chemie, 175, 2069-2077 (1974).
U.S. Pat. No. 5,532,289 discloses a process for forming a soft contact lens. According to the claims of this patent the lens is formed from a copolymer consisting essentially of 2,3-dihydroxypropyl methacrylate (i.e. glyceryl methacrylate [GMA]) and 2-hydroxyethyl methacrylate. Hydroxyethyl methacrylate is sometimes referred to as HEMA. The process of U.S. Pat. No. 5,532,289 requires a pre-distillation step wherein GMA is distilled. Hence, the process of U.S. Pat. No. 5,532,289 is laborious and costly.
WO 98/07055 discloses a process of preparing an ocular device (such as a contact lens) consisting essentially of GMA and HEMA, the process comprising the following steps: a) copolymerising a second monomer and a first monomer having attached to it a modifier group, thereby to form a first polymer having associated with it the modifier group; and b) modifying all or some the modifier group associated with the first polymer to form a second polymer different from the first polymer thereby to form the ocular device consisting essentially of GMA and HEMA.
The present invention seeks to overcome the problems associated with the known processes for preparing polymers.
According to a first aspect of the present invention there is provided a process for the preparation of a polymerisable monomer of formula I 
comprising the step of contacting a compound of formula II 
with an immobilised acid,
wherein X, Y, Z, R1, P and Q are independently selected from a hydrocarbyl group or hydrogen and wherein A is (CH2)n wherein n is 0 or 1.
According to a second aspect of the present invention there is provided an ocular device (such as a contact lens) prepared by the process according to the present invention.
According to a third aspect of the present invention there is provided an apparatus for a process for the preparation of a polymerisable monomer of formula I 
from a compound of formula II 
the apparatus comprising
(i) a means for containing an immobilised acid;
(ii) an inlet for a gas, wherein the inlet is configured such that, in use, the gas passes through the immobilised acid; and
(iii) means for removing the gas, comprising reaction product Pxe2x80x94C(O)xe2x80x94Q, from the means for containing the immobilised acid.
The present invention may provide a number of advantages.
The present invention has the advantage that the presence of impurities which act as cross-linkers during the polymerisation of the monomer is reduced or avoided. Thus, the present invention provides a monomer capable of polymerisation to form a straight chain polymer without the need to purify the monomer prior to polymerisation. Moreover, the monomer is capable of polymerisation to form a polymer which may be readily solubilised.
The present invention has the advantage that because of the absence of cross-linker or the low initial cross-linker concentration in the monomer, controlled additions of further cross-linker to achieve the desired/optimum level are possible. In contrast, if monomer e.g. GMA, in accordance with the prior art is used, the level of cross-linker is often already too high to allow further additions without detriment to the mechanical properties of the final polymer, such as a lens. This advantage of the present invention is demonstrated if GMA is polymerised. The resultant polymer may simply dissolve into a suitable solvent such as water.
In a further aspect there is provided the process of the present invention for the preparation of a composition comprising a polymerisable monomer of formula I.
It will be appreciated by a person skilled in the art that at least one of X, Y, Z or R1 is a polymerisable group such that the compound of formula I is a polymerisable monomer. In a preferred aspect, R1 is a polymerisable group.
In a preferred aspect of the process of the present invention the acid is a strong acid. By the term xe2x80x9cstrong acidxe2x80x9d it is meant an acid having a pKa of less than 3.
In a preferred aspect of the process of the present invention the acid is immobilised on an ion exchange resin. More preferably the acid is a strong acid immobilised on an ion exchange resin. Yet more preferably the ion exchange resin is Amberlyst 15, obtainable from Rxc3x6hm and Haas. of USA.
Preferably, R1 is selected from hydrocarbyl group, and hydrocarbyl esters, preferably unsaturated hydrocarbyl esters.
The term xe2x80x9chydrocarbyl groupxe2x80x9d as used herein means a group comprising at least C and H and may optionally comprise one or more other suitable substituents. Examples of such substituents may include halo-, alkoxy-, nitro-, hydroxy, carboxyl, epoxy, acrylic, hydrocarbon, N-acyl, or cyclic group etc. In addition to the possibility of the substituents being a cyclic group, a combination of substituents may form a cyclic group. If the hydrocarbyl group comprises more than one C then those carbons need not necessarily be linked to each other. For example, at least two of the carbons may be linked via a suitable element or group. Thus, the hydrocarbyl group may contain hetero atoms. Suitable hetero atoms will be apparent to those skilled in the art and include, for instance, sulphur, nitrogen and oxygen.
The term xe2x80x9chydrocarbyl esterxe2x80x9d as used herein means a hydrocarbyl group comprising axe2x80x94C(O)xe2x80x94Oxe2x80x94group.
The term xe2x80x9cunsaturated hydrocarbyl esterxe2x80x9d as used herein means a hydrocarbyl ester comprising at least one carbon-carbon double bond or at least one carbon-carbon triple bond.
Preferably, the hydrocarbyl group is a linear or a branched group. The branched group may contain one or more branches.
In one aspect, the linear or a branched hydrocarbyl group may contain from 1 to 20 carbon atoms, from 1 to 15 carbon atoms, from 1 to 10 carbon atoms, from 1 to 5 carbon atoms, or from 1 to 3 carbon atoms.
The linear or a branched hydrocarbyl group may be saturated or unsaturated. In one aspect, the linear or a branched hydrocarbyl group may saturated.
Preferably, the hydrocarbyl group comprises an alkyl backbone. The backbone may be interrupted by one or more non-alkyl groups. The non-alkyl groups may be selected from ester, ether and combinations thereof.
In one aspect, the alkyl backbone may contain from 1 to 20 carbon atoms, from 1 to 15 carbon atoms, from 1 to 10 carbon atoms, from 1 to 5 carbon atoms, or from 1 to 3 carbon atoms.
The alkyl backbone may contain one or more alkyl groups branched from the alkyl backbone. In one aspect, each alkyl branch may contain from 1 to 20 carbon atoms, from 1 to 15 carbon atoms, from 1 to 10 carbon atoms, from 1 to 5 carbon atoms, or from 1 to 3 carbon atoms.
The hydrocarbyl group may be a cyclic group. In this regard, the hydrocarbyl group can be a single ring group or a polycyclic group. Here, the term xe2x80x9cpolycyclicxe2x80x9d includes fused and non-fused ring structures including combinations thereof.
At least one of the cyclic groups of the polycyclic group may be a heterocyclic group (a heterocycle) or a non-heterocyclic group.
The cyclic group or at least one of the cyclic groups of the polycyclic group may be a saturated ring structure or an unsaturated ring structure (such as an aryl group).
The hydrocarbyl group may contain any one or more of C, H, O, Si, N, P, halogen (including Cl, Br and I), S and P. In the preferred aspect wherein the hydrocarbyl group comprises an alkyl backbone, the alkyl backbone may be interrupted by one or more of any one or more of C, H, O, Si, N, P, halogen (including Cl, Br and I), S and P.
Preferably, the hydrocarbyl group is a hydrocarbon group.
Here the term xe2x80x9chydrocarbon groupxe2x80x9d means any one of an alkyl group, an alkenyl group, an alkynyl group, an acyl group, which groups may be linear, branched or cyclic, or an aryl group. The term hydrocarbon also includes those groups but wherein they have been optionally substituted. If the hydrocarbon is a branched structure having substituent(s) thereon, then the substitution may be on either the hydrocarbon backbone or on the branch; alternatively the substitutions may be on the hydrocarbon backbone and on the branch.
The hydrocarbon group may have from 1 to 20 carbon atoms, from 1 to 15 carbon atoms, from 1 to 10 carbon atoms, from 1 to 5 carbon atoms, or from 1 to 3 carbon atoms.
In a preferred embodiment R1 is a group of formula III 
wherein R2 is selected from methyl, ethyl, propyl and butyl and R3 is selected from an unsaturated C1-5 alkyl. In a highly preferred embodiment R2 is CH3 and R3 is xe2x95x90CH2.
Preferably, X, Y, P and Q of formulae given in the present specification are independently selected from a hydrocarbyl group and hydrogen. Preferably, the hydrocarbyl group is a hydrocarbon group. More preferably the hydrocarbyl group is a hydrocarbon group having from 1 to 20 carbons. Yet more preferably, the hydrocarbyl group is selected from methyl, ethyl, propyl and butyl.
In a highly preferred embodiment X is H, Y is H, Z is H, P is CH3, Q is CH3, n=0, and R1 is a group of formula III, in which R2 is CH3 and R3 is xe2x95x90CH2.
Thus in a highly preferred aspect the present invention provides a process for the preparation of a polymerisable monomer of formula I 
comprising the step of contacting a compound of formula II 
with an immobilised acid,
wherein
X is H
Y is H
Z is H
A is (CH2)0 
P is CH3 
Q is CH3 
and wherein R1 is a group of formula III 
in which R2 is CH3 and R3 is xe2x95x90CH2.
In other words, in a highly preferred aspect, the present invention provides a process for the preparation of glyceryl methacrylate (GMA), comprising the step of contacting (2,2 1,3-dioxolan-4-yl) methyl methacrylate (GMAK) with an immobilised acid.
In a preferred embodiment of the present invention the process further comprises providing means for containing the immobilised acid, contacting the immobilised acid with the compound of formula II and passing a gas through the immobilised acid.
Preferably the gas contains oxygen. More preferably, the gas is air.
In a preferred embodiment of the present invention the immobilised acid is contacted with the compound of formula II in the absence of an organic solvent.
Preferably the means for containing the immobilised acid comprises a fluidised bed reactor.
In a further preferred aspect of the present invention the process comprises extracting the gas from the means for containing the immobilised acid after the gas has passed through the immobilised acid. The extracted gas may contain a reaction product of the contact of the compound of formula II with the immobilised acid. The reaction product may be of the formula Pxe2x80x94C(O)xe2x80x94Q. By removing the reaction product, the equilibrium II ⇄I+Pxe2x80x94C(O)xe2x80x94Q will be driven towards I. Thus the rate of conversion and/or ultimate conversion of I will be increased. An essentially quantitative conversion may be obtained.
In a preferred aspect the process of the present invention comprises the step of polymerising the polymerisable monomer of formula I. Any typical, suitable polymerisation method may be used. The preferred method is free radical polymerisation, thermal or UV initiated.
In a preferred aspect the process of the present invention further comprises the step of polymerising the polymerisable monomer of formula I to provide a medical device, in particular an ocular device such as a contact lens.
The present invention is very advantageous for preparing ocular devices, such as contact lenses (both hard and soft contact lenses), intraocular lenses, interocular lenses and intercorneal implants, as well as prostheses and hydrogel articles. In this regard, the present invention not only enables the ocular devices to be made more easily but also it allows a greater control over any one of the shrinkage, the dimensional consistency, the swell, the water sensitivity, the hydrophobicity or the hydrophilicity, or combinations thereof, of the resultant polymer.
The medical device and/or polymerisable monomer and/or composition may also comprise conventional additional components such as any one or more of emulsifiers, stabilisers, surface active agents, initiators (such as photoinitiators), inhibitors, dispersants, oxidising agents, reducing agents, viscosity modifiers, catalysts, binders, activators, accelerators, tackifiers, plasticizers, saponification agents, chain transfer agents, cross-linking agents, surfactants, fillers, dyes, metal salts, and solvents.
By way of example, the surfactants and dispersants can be salts of fatty rosin and naphthenic acids, condensation products of naphthalene sulphonic acid and formaldehyde of low molecular weight, carboxylic polymers and copolymers of the appropriate hydrophile-lipophile balance, higher alkyl sulfates, such as sodium lauryl sulfate, alkyl aryl sulfonates, such as dodecylbenzene sulfonate, sodium or potassium isopropylbenzene sulfonates or isopropylnaphthalene sulfonates; sulfosuccinates, such as sodium dioctylsulfosuccinate alkali metal higher alkyl sulfosuccinates, e.g sodium octyl sulfosuccinate, sodium N-methyl-N-palmitoyl-taurate, sodium oleyl isethionate, alkali metal salts of alkylarylpolyethoxyethanol sulfates or sulfonates, e.g. sodium t-octylphenoxy-polyethoxyethyl sulfate having 1 to 5 oxyethylene units. Typical polymerisation inhibitors that can be used include hydroquinone, monomethyl ether, benzoquinone, phenothiazine and methylene blue.
In a preferred embodiment the dye is selected from the group consisting of 2-hydroxybenzophenone, oxidiazoles, salicylic acid, resorcinol monobenzoate, benzotriazole, preferably 2H-benzotriazole, benzothiazoloazine, preferably 2N-benzothi-azoloazine, xcex1-cyano-xcex2-phenylcinnamic acid, polyalkypiperidine and derivatives thereof.
Preferably, the dye is selected from benzotriazole, in particular 2H-benzotriazole and derivatives thereof.
The composition and/or medical device of the present invention may comprise one or more additional comonomers. Examples of the one or more additional comonomers that can be used in the present invention include one of: (alkyl and cycloalkyl) acrylates; (alkyl and cycloalkyl) methacrylates; free-radical polymerisable olefinic acids, including alkoxy-, alkylphenoxy-, alkylphenoxy-(polyethyleneoxide)-, vinyl ester-, amine substituted (including quaternary ammonium salts thereof), nitrile-, halo-, hydroxy-, and acid substituted (for example phospho- or sulpho-) derivatives thereof; and other suitable ethylenically unsaturated polymerisable moieties; including combinations thereof Preferably the alkyl and cycloalkyl groups contain up to 20 carbon atoms, e.g. (C1-C20 alkyl and C1-C20 cycloalkyl) acrylates, and (C1-C20 alkyl and C1-C20 cycloalkyl) methacrylates. In more detail, typical comonomers include any one of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, isobomyl acrylate, pentyl acrylate, hexyl acrylate, octyl acrylate, iso-octyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate, eicosyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, cycloheptyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxymethylacrylate, hydroxymethylmethacrylate, propyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, pentyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, isobomyl methacrylate, heptyl methacrylate, cycloheptyl methacrylate, octyl methacrylate, iso-octyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, eicosyl methacrylate, dodecyl acrylate, pentadecyl acrylate, cetyl acrylate, stearyl acrylate, eicosyl acrylate, isodecyl crylate, vinyl stearate, nonylphenoxy-(ethyleneoxide)1-20 acrylate, octadecene, exadecene, tetradecene, dodecene, dodecyl methacrylate, pentadecyl methacrylate, cetyl methacrylate, stearyl methacrylate, eicosyl methacrylate, isodecyl methacrylate, nonylphenoxy-(ethyleneoxide)1-20 methacrylate, acrylic acid, methacrylic acid, fumaric acid, crotonic acid, itaconic acid, fumaric anhydride, crotonic anhydride, itaconic anhydride, maleic acid, maleic anhydride. styrene, alpha-methyl styrene, vinyl toluene, acrylonitrile, methacrylonitrile, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylamide, methacrylamide, methacrylamide 2-cyanoethyl acrylate, 2-cyanoethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylate t-butylaminoethyl methacrylate, glycidyl acrylate, glycidyl methacrylate, glyceryl acrylate, glyceryl methacrylate, benzyl acrylate, benzyl methacrylate, phenyl acrylate, phenyl methacrylate, vinyl pyridine, vinyl pyrrolidine, siloxanes, silanes and mixtures thereof. Other polymerisable monomers are disclosed in U.S. Pat. Nos. 2,879,178, 3,037,006, 3,502,627, 3,037,969 and 3,497,485.
Preferred comonomers include any one of glyceryl methacrylate (GMA), (2,2 dimethyl-1,3-dioxolanyl) methyl methacrylate (GMAK), hydroxy ethyl methacrylate (EMA), methacrylic acid, acrylic acid, GYMA, N-vinyl pyrrolidone, alkyl methacrylates (such as C1-20 alkyl methacrylates, more preferably C1-15 alkyl methacrylates, more preferably C1-10 alkyl methacrylates, more preferably C1-15 alkyl methacrylates, such as methyl methacrylate), alkyl acrylates (such as C1-20 alkyl acrylates, more preferably C1-15 alkyl acrylates, more preferably C1-10 alkyl acrylates, more preferably C1-5 alkyl acrylates, such as methyl acrylate), aryl methacrylates, aryl acrylates, diacetone acrylamide, acrylamide, methacrylamide, N-alkyl acrylamides (such as C1-20 N-alkyl acrylamides, more preferably C1-15 N-alkyl acrylarides, more preferably C1-10 N-alkyl acrylamides, more preferably C1-5 N-alkyl acrylamides, such as methyl acrylamide), N-alkyl methacrylamides (such as C1-20 N-alkyl methacrylamides, more preferably C1-15 N-alkyl methacrylamides, more preferably C1-10 N-alkyl methacrylamides, more preferably C1-5 N-alkyl methacrylamides, such as methyl methacrylamide), vinyl acetate, vinyl esters, styrene, other substituted olefins, N-dialkyl acrylamides (such as C1-20 N-dialkyl acrylamides, more preferably C1-15 N-dialkyl acrylamides, more preferably C1-10 N-dialkyl acrylamides, more preferably C1-15 N-dialkyl acrylamides, such as N N dimethyl acrylamide), N-dialkyl methacrylamides (such as C1-20 N-dialkyl methacrylamides, more preferably C1-15 N-dialkyl methacrylamides, more preferably C1-10 N-dialkyl methacrylamide, more preferably C1-15 N-dialkyl methacrylamides, such as N N dimethyl methacrylamide), 3-methacryloxypropyl tris (trimethysilyl siloxy) silane (TRIS monomer), fluoro substituted alkyl and aryl acrylates and methacrylates (preferably wherein the alkyl is C1-20 alkyl, more preferably C1-15 alkyl, more preferably C1-10 alkyl, more preferably C1-5 alkyl), and combinations thereof.
More preferred comonomers include any one of glyceryl methacrylate (GMA), (2,2 dimethyl-1,3-dioxolan-4-yl) methyl methacrylate (GMAK), 2-hydroxy ethyl methacrylate (2-HEMA), methacrylic acid and acrylic acid, or combinations thereof.
The lists of comonomers also include substituted derivatives of those monomers, such as halogenated monomers, especially fluorinated monomer derivatives, and acetal and ketal derivatives.
The polymerisable monomer of the present invention and the one or more additional comonomers may be selected so that the composition and/or ocular device of the present invention consists essentially of GMA and HEMA.
In a preferred aspect the present invention also provides an ocular device (such as a contact lens) obtained by the process of the present invention wherein the ocular device comprises HEMA in amounts of from 80-20%; GMA in amounts of from 20-80% by weight; and optionally a cross-linking polymerised monomer in an amount of 5% or less; and wherein the ocular device contains less than 0.01% methacrylic acid.
In a preferred aspect of the present invention the compound of formula II is a derivative of GMA such as (2,2-dimethyl-1,3-dioxolan-4-yl) methyl methacrylate (GMAK). GMAK can be prepared following the teachings of Mori et al ([1994] Macromolecules 27 pp 35-39) and Oguchi et al Polym Eng. Sci. ([1990] 30 449). This preferred process of the present invention is also of particular interest as GMAK can be readily synthesised from cheap, commercially available materials and it can be prepared in a pure state, i.e. free from the substances normally present in commercial GMA, especially cross-linking substances.
Thus, in one aspect of the present invention the compound of formula II is or is part of a polymer. However, as explained above, the compound of formula II is preferably a monomer.
A polymer prepared in accordance with the present invention may be fabricated as buttons or cast moulded or spun cast lenses.
As discussed above, in one aspect the present invention provides an apparatus for use in a process as described above. The present invention provides an apparatus for a process for the preparation of a polymerisable monomer of formula I 
from a compound of formula II 
the apparatus comprising
(i) a means for containing an immobilised acid;
(ii) an inlet for a gas, wherein the inlet is configured such that, in use, the gas passes through the immobilised acid; and
(iii) means for removing the gas, comprising reaction product Pxe2x80x94C(O)xe2x80x94Q, from the means for containing the immobilised acid.
Each of the preferred features given above in respect of the process of the present invention, equally apply to the apparatus of the present invention.
It will be appreciated that reaction product Pxe2x80x94C(O)xe2x80x94Q is a volatile compound. By the term xe2x80x9cvolatile compoundxe2x80x9d we mean that the compound which has a boiling point and standard temperature and pressure of less than 150xc2x0 C. or a compound which may form an azeotrope with water.
The present apparatus is advantageous because by removing the reaction product, the equilibrium II⇄I+Pxe2x80x94C(O)xe2x80x94Q will be driven towards I. Thus the yield of I will be increased. An essentially quantitative yield may be obtained.
By use of the apparatus of the present invention with the preferred compounds of the process of the present invention, extremely high conversions have been achieved. When GMAK was contacted with immobilised acid,  greater than 99.9% conversion was achieved.
The apparatus of the present invention is advantageous because high yields of monomer suitable for processing without further purification may be obtained utilising simple apparatus. The provision of gas through an immobilised acid ensures good contact between the compounds of the process and the acid. In the preferred aspect of the present invention wherein the immobilised acid is in the form of an ion exchange resin, the gas agitates the resin ensuring good contact between the resin and the reactants. Moreover, in the preferred aspect of the present invention wherein the gas contains oxygen, the presence of the oxygen prevents polymerisation of polymerisable monomer I of the present invention.
When a compound of formula II is contacted with an immobilised acid to provide a polymerisable monomer of formula I, an acid may be formed by the reaction. For example, when (2,2 dimethyl-1,3-dioxolan-4-yl) methyl methacrylate (GMAK) is contacted with immobilised acid to provide GMA, methacrylic acid is formed in small amounts. In a preferred aspect of the present invention, the acid is not subsequently neutralised. In an alternative preferred aspect, wherein the present invention provides a composition comprising a polymerisable monomer of formula I, the process further comprises the step of polymerising the polymerisable monomer of formula I, with the proviso that the polymerisable monomer composition is not neutralised prior to polymerisation. In preferred aspects of the present invention, the acid is methacrylic acid or acrylic acid.
The omission of the neutralisation of any acid avoids and/or reduces the formation of cross-linker. For example, in the aspect in the present invention described above wherein GMAK is contacted with an immobilised acid to form GMA, if methacrylic acid present in the composition comprising GMA is neutralised, glycerol dimethacrylate is formed (DGMA). Glycerol dimethacrylate is a cross-linker.
Thus in a further aspect, the present invention provides a process for the preparation of a polymer, comprising the steps of
(i) contacting a compound of formula II 
with an immobilised acid,
wherein X, Y, Z, R1, P and Q are independently selected from a hydrocarbyl group or hydrogen and wherein A is (CH2)n, wherein n is 0 or 1;
such that a polymerisable monomer of formula I is provided 
and
(ii) polymerising the polymerisable monomer of formula I, with the proviso that any acid present in the polymerisable composition is not neutralised prior to polymerisation.